Driving cap for drivepin, and tool and method therefor

ABSTRACT

A DRIVEPIN HAVING A DRIVING CAP ON ONE END, AND A TOOL FOR POSITIONING THE DRIVEPIN IN ABUTTING ENGAGEMENT WITH A HARD WORK SURFACE. A RAMROD IN THE TOOL IGNITES A PROPELLANT CONTAINED IN THE DRIVING CAP TO DRIVE THE DRIVEPIN INTO THE WORK SURFACE. A CUSHIONING PAD IN THE DRIVING CAP EXPANDS TO FORM A GAS TIGHT SEAL WITHIN THE TOOL FOR REDUCING NOISE.

Feb. 1971 YUNG SHING HSU DRIVING CAP FOR DRIVEPIN, AND TOOL AND METHODTHEREFOR 2 Sheets-Sheet 1 Filed Sept. 16. 1968 A TTOAZA/E Y YUNG SHINGHSU Feb. 2, 1971 v DRIVING CAP DRIVEPIN, AND I'OOL AND METHOD THEREFORFiled Sept. 16 1968 2 She'ts-Sheet 2 INVENTOE YLJNG s/-///-/c; A/SUUnited States Patent 3,559,272 DRIVING CAP FOR DRIVEPIN, AND TOOL ANDMETHOD THEREFOR Yung Shing Hsu, Milwaukie, Oreg., assignor to OmarkIndustries, Inc., Portland, Oreg. Filed Sept. 16, 1968, Ser. No. 759,855Int. Cl. B23p 11/00 US. Cl. 29-432 6 Claims ABSTRACT OF THE DISCLOSUREHISTORY OF THE INVENTION This invention relates to a method and meansfor driving drivepins into a hard surface.

Manually driving fastening pins, studs, bolts, nuts and the like(hereafter collectively referred to as drivepins) such as for fasteningmetal fixtures to concrete flooring in the construction of largecommercial buildings is slow and inadequate. Thus, there has beendeveloped for the construction industry a variety of explosivelyactuated tools for driving such drivepins.

Explosively actuated driving tools have heretofore been comprised of twogeneral types. One is referred to as the low-velocity driving tool andthe other as the highvelocity driving tool. The low-velocity drivingtool is adapted to receive a drivepin at the exit end of a cylindricalbarrel with a piston located inwardly and spaced from the drivepin. Anexplosive charge located behind the piston, i.e., at the breech end ofthe barrel, is detonated by a firing mechanism which rapidly acceleratesthe piston toward the drivepin. See for example, the commonly assignedKopf et a1. U.S. Pat. No. 2,239,121 issued on Mar. 8, 1966 on a PistonPowder Actuated Tool. The high-velocity tool is adapted to receive adrivepin at the breech end of the barrel. A charge is exploded directlyagainst the head of the drivepin to rapidly accelerate the drivepin infree flight down the length'of the barrel and at the work surface. Seefor example the commonly assigned Kopf et a1. U.S. Pat. No. 3,221,966issued on Dec. 7, 1965.

High-velocity tools have the disadvantage of high noise level, dangerousfree fastener velocity, and high degree of spall and ricochet when thedrivepin strikes the work surface. Low-velocity tools have thedisadvantage of high noise level, power limitation, severe spall out inconcrete, and high incidence of drivepin damage. The preferredembodiment of the present invention is thus adapted to provide animproved method and means for driving a drivepin which has the drivingcapacity of a high-velocity tool and the safety of the low-velocity toolas well as the unique characteristics of simplicity, low noise level andreduced drivepin and work damage.

SUMMARY OF THE INVENTION In general, the preferred embodiments of theinvention comprises a drivepin with a driving cap attached to the headof the drivepin. The driving cap includes a propellant in the form of apower pill and a cushioning pad that functions as a silencer. The toolfor driving the drivepin is adapted to receive the drivepin at the exitend of an open ended barrel. When the tool is placed against a worksurface the pointed end of the pin is abutted against the work surface.A ramrod slidable within the barrel of the tool is adapted to be drivenagainst the driving cap. The hard work surface provides a rigidresistance to the pin and upon driving the ramrod against the power pillof the driving cap from the opposite end, the impulse ignites thepropellant. The energy of the propellant is transmitted to the head ofthe drivepin and propels the drivepin into the hard work surface. Thecushioning pad being compressed against the drivepin expands or bulgeswithin the barrel to form a gas tight seal.

With the drivepin abutted against the work surface, the energy of thepower pill is directly applied to force a penetration of the drivepininto the work surface. This is believed to be an important departurefrom prior art devices wherein an explosion first produces a rapidvelocity in free flight on either a piston (low-velocity tool) ordrivepin (high-velocity tool), with the kinetic energy of the rapidvelocity producing the penetrating force. Also, the sealing effect ofthe cushioning pad renders the driving operation relatively noiseless.Other benefits and advan tages of the invention will become apparent byreference to the following detailed description and drawings wherein:

FIG. 1 is a perspective view with portions broken away illustrating thetool and operation of driving a drivepin into a concrete slab inaccordance with the invention;

FIG. 2 is a cross sectional view of the tool used in the drivingoperation of FIG. 1;

FIG. 3 is a partially sectioned view of a drivepin having a driving capattached thereto in accordance with the invention;

FIG. 4 is a partial view further illustrating the driving operation withthe drivepin partially driven into the hard work surface;

FIG. 5 illustrates a modification to the drivepin; and

FIG. 6 illustrates a further modification to the drivepin.

DETAILED DESCRIPTION Referring to FIGS. 1 and 2 of the drawings, adriving tool 10 has an outer housing which serves as a handle 12, e.g.of molded plastic or the like. A tubular insert 14 in the handle 12 isconstructed of a hard material, e.g. steel, and forms an open endedbarrel 16 for the driving tool 10. The tubular insert 14 extends belowthe handle portion 12, and a guard fixture 18 is assembled to the handleportion 12, and is co-extensive with the extended end of the tubularinsert 14. (As used hereafter, up and down, top and bottom, and similardirectional terms are all with reference to the positioning of the toolas shown in FIG. 1. It is to be understood, however, that the tool maysimilarly be used on side walls, ceiling, etc.) The guard fixture 18 hasa flared bottom portion which aids the user in positioning the toolsquarely against a work surface 20 (see FIG. 1). A noiseproof lining 22is molded to the inside of the flared portion of the guard fixture 18.

A ramrod 26 within the barrel 1-6 is generally circular in cross sectionwith a lower portion 28 that is adapted to conform closely to the lowersection of the barrel 16. A flange 30 above the lower portion 28 of theramrod 26 is tapered so as to seat against a tapered entry 24 of thebarrel 16 as shown in FIG. 2. A retaining cap 32 is threadedly engagedwith the top of the tubular insert 14 land is adapted to permit slidingmovement therethrough of the main portion of the ramrod 26 but not theflange 30. Thus the sliding movement of the ramrod 26 within the barrel16 is limited in its upward movement by the flange 30 being abuttedagainst the retaining cap 32, and is limited in its downward movement bythe flange 30 being seated against the tapered entry 24 of the barrel16. A knob 34 is afiixed to the top of the ramrod 26 and is adapted tobe struck by a hammer 36 or the like as schematically illustrated inFIG. 1.

A drivepin 38 for the illustrated driving operation of FIG. 1 is shownin FIG. 3. The drivepin 38 is comprised of a shank with a point at oneend and a head 40 at the other end. A driving cap 42 is attached to thehead 40 of the drivepin 38. The driving cap 42 is comprised of acylindrical pad 44 with an inset portion at one end adapted to fit overthe head 40 of the drivepin 38 and an inset portion at the other endadapted to receive a power pill 46. A washer 41 of deformable materialis attached to the shank of the drive pin adjacent the pointed end. Thewasher 41 provides a light frictional gripping action for holding thedrivepin inside the barrel 16, and also in cooperation with the head 40and driving cap 42 aligns the drive pin along the axis of the barrel 16(see FIG. 1).

The drivepin 38 is formed from a hard metal such as steel.The materialof the cushioning pad 44 is deformable under impact so as to expand orbulge against the wall of the barrel 16 to tightly seal against gasleakage (see FIG. 4). A suitable material for the cushioning pad is asoft grade of aluminum such as aluminum 1100. Other suitable materialsinclude plastics such as Teflon, available from E. I. du Pont de NemoursCompany. A lubricant 48 is coated on the outside of the aluminumcushioning pad 44 to minimize the friction between the aluminum pad 42and the steel wall of the barrel 16. A suitable lubricant is the productknown as Industrial Teflon Coating also available from E. I. du Pont deNemours Company. It will be understood however that a plastic pad may beself lubricating.

The power pill 46 is selected to have the properties of high energyoutput preferably in the range of about 40 to 300 foot/pounds. Thepreferred propellant material is one that can be contained in a smallvolume, will ignite by a high impulse, e.g. one pound second, and issufliciently stable so as not to be ignited at a lower impulse or byfriction such as might be encountered in mishandling of the pins or aloaded tool. Also these conditions should remain constant for asubstantial shelf life period. A suitable propellant for the power pillis composed of compacted nitrocellulose fibres having a density of about1 gram per cubic centimeter.

OPERATION In operation, the fastening pin 38 with the driving cap 42attached thereto, is inserted into the exit end of the barrel 16 of thedriving tool 10, as shown in FIG. 1 of the drawings. The driving tool 10is positioned against the work surface 20 with the guard fixture 18aiding in the proper alignment of the barrel with the work surface 20.The ramrod 26 is then moved against the driving cap 42 to push thedrivepin 38 tightly against the work surface 20. The hammer 36 is usedto strike the knob 34 of the ramrod 26 which strikes the power pill 46in the driving cap 42 which creates the suflicient impulse to releasethe energy of the propellant. Reliable ignition will be achieved from a2 pound hammer swing at a rate of 10l5 feet/second thereby producing anappropriate pound/second value. The energy of the propellant istransmitted to the drivepin 38 through the pad 44 to drive the drivepininto the work surface 20.

Although we do not wish to be bound by this theory, it is believed thatan important feature for igniting the relatively stable propellantmaterial of the power pill is the protrusion 29 on the end of the ramrod28. This protrusion initially causes a shearing force on the center areaof the pill and because the following peripherial area 29-c'ontains thematerial being sheared and prevents it from flowing away from theprotrusion, frictional heat is generated to cause the desired ignition.The protrusion 45 of the cushioning pad 44 is believed to provide asimilar shearing function as the pill is forced against the deformablematerial at the peripherial area 45'.

The penetration of the drivepin into the work surface 20 is illustratedin FIG. 4 of the drawings. As shown, the propellant forces axialcompression of the pad 44 with a resulting lateral expansion or bulging.This bulging of the pad 44 forms a gas tight seal around the driving cap42. This sealing off of the gasses renders the tool substantiallynoiseless. The driving cap breaks away from the head of the drivepin atthe end of the power stroke and remains solidly expanded within thebarrel of the tool. The lubricant coating on the exterior of the drivingcap allows it to be ejected from the barrel by driving the ramrodagainst the driving cap with the hammer.

A significant safety factor is believed to be achieved by the invention.The propellant requires a substantial impulse before it will detonate,and it is inert to static compression. Thus until the tool is positionedso as to abut the drivepin against a hard work surface, the ramrodcannot ignite the propellant. Ramming the propellant of the fasteningpin without the rigid resistance of the work surface will only result ina manual driving of the drive pin (with propellant intact) out of thebarrel. Also, with the drivepin abutted against the work surface, thepropellant drives the drivepin directly into the work surface and thevelocity of the drivepin as it is driven into the work surface issubstantially less than the velocity of a drivepin or piston in freeflight as in the prior devices. For safety purposes this can beimportant in instances where excessively hard objects, such as pieces ofmetal or stone that are embedded in a concrete slab, lie in the path ofthe drivepin. If the pin strikes at a very high velocity, as in theprior devices, the ricocheting of the pin from such hard objects can bedangerous.

A further advantage is believed realized in the attainment of muchgreater efiiciency of the driving force. First because the propellantenergy is applied directly to the driving of the drivepin, and secondbecause the ramrod, after igniting the power pill 46, follows thedrivepin down the barrel 16. The moving ramrod inhibits the gasexpansion within the chamber resulting in increased energy being appliedto the drivepin.

An alternative embodiment of the drivepin and driving cap is illustratedin FIG. 5 of the drawings. The power pill 46 is placed adjacent to thehead 40 of the drivepin 38 and a suitable wrapping 50 secures the powerpill to the drivepin. Whereas a similar driving force is achieved ascompared to the driving cap having a cushioning pad, the benefits ofnoiselessness may be sacrificed. Another embodiment is shown in FIG. 6where a drivepin 52 is provided with a head 54 having an inset providedtherein for receiving a power pill 46.

Other alternatives and modifications will be apparent to those skilledin the art without departing from the scope of the invention. Thus theabove described embodiments of the invention are intended to set forthpreferred examples of the invention and are not intended to limit thescope thereof which is defined in the following claims.

What is claimed is:

1. A driving cap comprising a deformable cylindrically shaped cushioningpad adapted to be placed on the head of a drivable member, a power pillembedded in the cushioning pad opposite the drivable member, said powerpill being ignited at no less than one pound second impulse.

2. A driving cap comprising a deformable cylindrically shaped cushioningpad adapted to be placed on the head of a drivable member, a power pillembedded in the cushioning pad, and means between the power pill andcushioning pad to assist the ignition of the power pill.

3. A driving cap as defined in claim 2 wherein a cavity is formed in theend of the cushioning pad, said ignition assistance means comprising aprotrusion in the bottom of the cavity, said power pill being in thecavity abutted against the protrusion and spaced from the boltom of thecavity.

4. A driving cap as defined in claim 3 whereby said power pill has alevel of ignition no less than one pound second impulse.

5. A driving cap as defined in claim 2 wherein the power pill iscomposed of compacted nitrocellulose fibres having a density of aboutone gram per cubic centimeter.

6. A method of driving a drivepin into a hard work surface whichincludes placing a driving cap including an expandable pad and powerpill on the head of a drive pin with the expandable pad between the headof the drivepin and the pill, confining the drivepin with driving cap inthe barrel of a tool, abutting the drivepin against a solid work surfaceand striking the power pill with a ramrod to create sufiicient impulsefor axially compressing the pad to cause peripheral expansion forsealing off gasses and then igniting the power pill to thereby drive thedrivepin into the work surface While continuing the axial compression ofthe pad.

References Cited UNITED STATES PATENTS 6/ 1909 Gehne 227147 1/ 1921Temple 227-9 11/ 1951 Temple 227-9 4/1957 Henning et a1 22711 1/1960DeCaro 10238 7/1963 Turner 10239 6/ 1964 Rosenberg, Jr 8510 6/ 1967Hilti 29432 3/ 1968 Kvavle 227 9UX 8/1968 Kvavle 22710 8/ 1968 Kvalve102--3 8X US. Cl. X.R.

